A spectroelectrochemical study on polaron transformations in polyaniline in sulphuric andp-toluenesulphonic acids

Abstract

The electrochemical processes involved in the oxidation of polyaniline in sulphuric and p-toluenesulphonic acids were studied under steady potential and during a potentiostatic current transient using UV-Vis absorption spectroscopy. It was found that sulphate ions are reversibly inserted into the polymer film on oxidation and removed during reduction, while tosylate ions are irreversibly accumulated slowly in the film and protons are exchange instead. The redox peaks involve two independent transformation equilibria of three main species: reduced species, polaron and bipolaron of different chain lengths. While the charge involved in the polaron transformation is less than 20% of the charge involved safely in the oxidation of polyaniline before the onset of degradation, a significant capacitive contribution 40-60% was detected before the start of further oxidation of the polaron to bipolarons. Nernstian analysis of the redox process was possible only for the reverse scan and with the absorption peak of the reduced form. The spectroscopic transients showed that the oxidation, which is much slower than the reduction, is essentially the same in both acids without a significant contribution of the diffusion of dopant species in contrast with the reduction process.